The invention relates to a communication arrangement as defined in the pre-characterizing part of claim 1.
Such a communication arrangement has been developed and marketed by the applicants and is therefore known.
In the known communication arrangement, a data source delivers data in the form of a sequence of logic ones and zeroes to modulation means. Furthermore, a high-frequency carrier signal, which can be produced by a carrier signal generator is fed to the modulation means. The modulation means modulate the carrier signal in accordance with the data and deliver a modulated carrier signal to an antenna current drive belonging to the modulation means. The antenna current drive has a fixed gain. The antenna current drive further has on the input side a high input resistance so as not to burden or distort the modulated carrier signal. On the side of the output, the antenna current drive has a nominally constant and low output resistance for driving an antenna current via an antenna circuit input resistance of typically several dozen Ohms.
The data source, the carrier signal generator and the modulation means are realized as component parts of an integrated circuit. With a design of the communication arrangement for transmitting data over a distance of up to 10 cm, the antenna current drive is realized as a discretely built two-stage C-amplifier separated from the integrated circuit because of the dissipation power that shows up, with which amplifier an adequate transmission power of the communication station may easily be achieved. For the reliable operation the antenna current drive further has appropriately dimensioned cooling means and stabilizing means for combating an undesired temperature drift.
In the known communication arrangement the modulation which can be performed with the modulation means is based on the principle of amplitude modulation. In dependence on the data, the amplitude of the carrier signal is changed then. For this purpose, the carrier signal is applied to two parallel-arranged buffer amplifiers which have an identical gain. The first buffer amplifier is driven with a first supply voltage and the second buffer amplifier is driven with a second supply voltage. For performing the amplitude modulation in dependence on the data, either the first buffer amplifier or the second buffer amplifier is connected to the antenna current drive, so that two different amplitudes of the carrier signal to be amplified are present on the input side of the antenna current drive in a time sequential manner.
The first supply voltage of the first buffer amplifier is fixed and the second supply voltage is generated via voltage values which are preprogrammed in an EEPROM. This basically realizes an amplitude modulation of the carrier signal with different degrees of modulation.
The use of two buffer amplifiers and the generation of the second supply voltage according to the voltage values preprogrammed in the EEPROM implies considerable circuitry and cost in the known communication arrangement and guarantees only a relatively coarse possibility of changing the degree of modulation. Furthermore, the antenna drive can only be adapted to various antenna circuits with difficulty and with considerable expenditure. The design of the antenna drive as a C-amplifier to guarantee the necessary transmission powers is the further obstruction to an integration of the antenna drive with the further components of an integrated circuit of the communication arrangement. In practice, however, in connection with such a communication arrangement as defined in the pre-characterizing part of claim 1, there has often been the desire to have a complete integration of the modulation means. Furthermore, it is desired that the modulation means must also have a considerably simpler design.